Generally, the more detailed the zoom, the more accurate the data – taking into account that the possible differences in lower-zoom values depend on weather conditions in the given area (values from many more tiles are averaged), not just the given spot (with only 1 tile interpreted). You can also check this comment. Anyway, the picker is not meant to be the most reliable weather indicator on Windy.

The most accurate weather indicator is the forecast detail for any spot (the detailed chart).

@thebigmuzzy
There is no need to zoom to a level lesser than the model's resolution.
e.g. ECMWF has a resolution of 9 km.
Do not expect reliable changes in locations less than 9 km apart.
Only interpolated values.